Phased generation and delivery of structured documents

ABSTRACT

In one embodiment, a method includes receiving a request for a web page; sending a first response portion for generating the requested web page to a client computing device that includes a structured document place-holder code segments and executable code for implementing a page-assembling process; generating second response portions each for generating a corresponding portion of the requested web page that each include a call to a function of the page-assembling process; determining relative priorities of the second response portions; sending the second response portions to the client computing device in an order based on the determined relative priorities; and wherein the page-assembling process is configured to insert, or cause to be inserted, at a location determined by a corresponding one of the place-holder code segments, the second portions of content into a model representation of the structured document generated by a client rendering application.

PRIORITY

This application is a continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 14/300,075, filed 9 Jun. 2014, which is acontinuation under 35 U.S.C. § 120 of U.S. patent application Ser. No.12/754,549, filed 5 Apr. 2010, issued as U.S. Pat. No. 8,751,925 on 10Jun. 2014, both of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to serving structured documents(such as web pages) to remote clients and, more particularly, to usingphased generation and delivery of structured documents for use inefficiently rendering structured documents and decreasing perceivedrendering time.

BACKGROUND

Conventionally, when a request for a web page or other structureddocument transmitted by a client device is received by a server orcomputing system hosting the web page, the hosting system typicallygenerates a base web page in the form of an Hyper Text Markup Language(HTML), Extensible Markup Language (XML), or other web browser-supportedstructured document. The generated structured document is thentransmitted in a response to the requesting client via a HypertextTransfer Protocol (HTTP) or other suitable connection for rendering atthe client device. The structured document may include one or moreresources (e.g. a JavaScript script or resource, a Cascading Style Sheet(CSS) resource, an image, a video, etc.), or references to suchresources, embedded within the transmitted document. By way of example,a resource embedded in an HTML document may generally be included orspecified within a script element, image element, or object element,among others, depending on the type of resource. The element referencingor specifying the resource may include a source attribute (e.g., src)identifying a location of the resource to the client requesting the webpage. Typically, upon receipt of the response, the web browser or otherclient application running at the client device then constructs adocument object model (DOM) representation of the received structureddocument and requests the resource(s) (which may be at one or more otherexternal locations) embedded in the document.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example network environment.

FIG. 2 illustrates a block diagram of example components of the examplenetwork environment of FIG. 1.

FIG. 3 shows a flowchart illustrating an example method for serving arequest for a web page.

FIG. 4 shows a flowchart illustrating an example method for executing apagelet callback function.

FIG. 5 shows a flowchart illustrating an example method for enforcing anorder of executing pagelet callback functions.

FIG. 6 illustrates an example computer system architecture.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The present disclosure relates generally to serving structured documentsto remote clients and, more particularly, to using phased generation anddelivery of structured documents for use in efficiently renderingstructured documents and decreasing perceived rendering time. Particularembodiments relate to a phased approach to serving a requestedstructured document, such as a web page. In particular embodiments, whena request for a particular web page is received by a host server orsystem, the host generates and transmits to the requesting client aninitial response or initial response portion that includes a “base” or“skeletal” structured document including markup language code forrendering one or more place-holders, as well as executable code thatwhen received by the client, implements a client-side page-assemblingprocess. After the initial response is received by the client, aclient-side document-rendering application renders the base structureddocument, which generally includes generating a model representation ofthe base structured document including the place-holders. In particularembodiments, the initial response further includes one or more resourcesor one or more references to resources to be downloaded and executed bythe document-rendering application.

In particular embodiments, after generating and transmitting the initialresponse, the host then launches one or more server-side page- orsubpage-generating processes that each generate a respective secondaryportion of the requested web page including markup language code (e.g.,HTML), one or more second resources, or one or more references to secondresources to be downloaded. Once a page-generating process completes asecondary portion of the requested web page, the secondary portion maythen be transmitted to the client in a secondary response or secondaryresponse portion. In an alternate embodiment, the host may generate eachsecondary portion sequentially in-process, which may generally notinvolve launching one or more other page-generating processes. Inparticular embodiments, after each of one or more secondary responsesare received, the client-side page-assembling process may dynamicallyinsert, or cause the client-side document-rendering application toinsert, the secondary portion of the requested web page received in thesecondary response, into the model representation at a correspondingplace-holder of the model representation for rendering by thedocument-rendering application. In this way, the client may render thebase structured document and at least start downloading the resourcesidentified in the initial response, such as embedded scripts and stylesheets, while the rest of the web page (included in the remaining one ormore secondary portions) is being generated by the host, therebypotentially reducing the time required to render the web page at theclient.

In various example embodiments, one or more described web pages may beassociated with a social networking system. However, alternateembodiments may generally have application to the retrieval andrendering of structured documents hosted by any type of networkaddressable resource or web site. Additionally, as used herein, a “user”may be an individual, a group, or an entity (such as a business or thirdparty application). Furthermore, as used herein, “or” may imply “and” aswell as “or;” that is, “or” does not necessarily preclude “and,” unlessexplicitly stated or implicitly implied.

Particular embodiments may operate in a wide area network environment,such as the Internet, including multiple network addressable systems.FIG. 1 illustrates an example network environment, in which variousexample embodiments may operate. Network cloud 60 generally representsone or more interconnected networks, over which the systems and hostsdescribed herein can communicate. Network cloud 60 may includepacket-based wide area networks (such as the Internet), privatenetworks, wireless networks, satellite networks, cellular networks,paging networks, and the like. As FIG. 1 illustrates, particularembodiments may operate in a network environment comprising socialnetworking system 20 and one or more client devices 30. Client devices30 are operably connected to the network environment via a networkservice provider, a wireless carrier, or any other suitable means.

In one example embodiment, social networking system 20 comprisescomputing systems that allow users to communicate or otherwise interactwith each other and access content, such as user profiles, as describedherein. Social networking system 20 is a network addressable systemthat, in various example embodiments, comprises one or more physicalservers 22 and data store 24. The one or more physical servers 22 areoperably connected to computer network 60 via, by way of example, a setof routers and/or networking switches 26. In an example embodiment, thefunctionality hosted by the one or more physical servers 22 may includeweb or HTTP servers, FTP servers, as well as, without limitation, webpages and applications implemented using Common Gateway Interface (CGI)script, PHP Hyper-text Preprocessor (PHP), Active Server Pages (ASP),Hyper Text Markup Language (HTML), Extensible Markup Language (XML),Java, JavaScript, Asynchronous JavaScript and XML (AJAX), and the like.

Physical servers 22 may host functionality directed to the operations ofsocial networking system 20. By way of example, social networking system20 may host a website that allows one or more users, at one or moreclient devices 30, to view and post information, as well as communicatewith one another via the website. Hereinafter servers 22 may be referredto as server 22, although server 22 may include numerous servershosting, for example, social networking system 20, as well as othercontent distribution servers, data stores, and databases. Data store 24may store content and data relating to, and enabling, operation of thesocial networking system as digital data objects. A data object, inparticular implementations, is an item of digital information typicallystored or embodied in a data file, database or record. Content objectsmay take many forms, including: text (e.g., ASCII, SGML, HTML), images(e.g., jpeg, tif and gif), graphics (vector-based or bitmap), audio,video (e.g., mpeg), or other multimedia, and combinations thereof.Content object data may also include executable code objects (e.g.,games executable within a browser window or frame), podcasts, etc.Logically, data store 24 corresponds to one or more of a variety ofseparate and integrated databases, such as relational databases andobject-oriented databases, which maintain information as an integratedcollection of logically related records or files stored on one or morephysical systems. Structurally, data store 24 may generally include oneor more of a large class of data storage and management systems. Inparticular embodiments, data store 24 may be implemented by any suitablephysical system(s) including components, such as one or more databaseservers, mass storage media, media library systems, storage areanetworks, data storage clouds, and the like. In one example embodiment,data store 24 includes one or more servers, databases (e.g., MySQL),and/or data warehouses.

Data store 24 may include data associated with different socialnetworking system 20 users and/or client devices 30. In particularembodiments, the social networking system 20 maintains a user profilefor each user of the system 20. User profiles include data that describethe users of a social network, which may include, for example, propernames (first, middle and last of a person, a trade name and/or companyname of a business entity, etc.) biographic, demographic, and othertypes of descriptive information, such as work experience, educationalhistory, hobbies or preferences, geographic location, and additionaldescriptive data. By way of example, user profiles may include a user'sbirthday, relationship status, city of residence, and the like. Thesystem 20 may further store data describing one or more relationships orconnections between different users. The relationship information mayindicate users who have similar or common work experience, groupmemberships, hobbies, or educational history. A user profile may alsoinclude privacy settings governing access to the user's information isto other users.

Client device 30 is generally a computer or computing device includingfunctionality for communicating (e.g., remotely) over a computernetwork. Client device 30 may be a desktop computer, laptop computer,personal digital assistant (PDA), in- or out-of-car navigation system,smart phone or other cellular or mobile phone, or mobile gaming device,among other suitable computing devices. Client device 30 may execute oneor more client applications, such as a web browser (e.g., MicrosoftWindows Internet Explorer, Mozilla Firefox, Apple Safari, Google Chrome,and Opera, etc.), to access and view content over a computer network. Inparticular implementations, the client applications allow a user ofclient device 30 to enter addresses of specific network resources to beretrieved, such as resources hosted by social networking system 20.These addresses can be Uniform Resource Locators, or URLs. In addition,once a page or other resource has been retrieved, the clientapplications may provide access to other pages or records when the user“clicks” on hyperlinks to other resources. By way of example, suchhyperlinks may be located within the web pages and provide an automatedway for the user to enter the URL of another page and to retrieve thatpage.

A web page or resource embedded within a web page, which may itselfinclude multiple embedded resources, may include data records, such asplain textual information, or more complex digitally encoded multimediacontent, such as software programs or other code objects, graphics,images, audio signals, videos, and so forth. One prevalent markuplanguage for creating web pages is the Hypertext Markup Language (HTML).Other common web browser-supported languages and technologies includethe Extensible Markup Language (XML), the Extensible Hypertext MarkupLanguage (XHTML), JavaScript, Cascading Style Sheet (CSS), and,frequently, Java. By way of example, HTML enables a page developer tocreate a structured document by denoting structural semantics for textand links, as well as images, web applications and other objects thatcan be embedded within the page. Generally, a web page may be deliveredto a client as a static document; however, through the use of webelements embedded in the page, an interactive experience may be achievedwith the page or a sequence of pages. During a user session at theclient, the web browser interprets and displays the pages and associatedresources received or retrieved from the website hosting the page, aswell as, potentially, resources from other websites.

More particularly, HTML enables developers to embed objects orresources, including web applications, images, or videos, within astructured document such as a web page. Generally, an HTML structureddocument is written in the form of HTML elements that consist of tags(surrounded by angle brackets) within the structured document content,which act as indicators to a web browser rendering the structureddocument as to how the document is to be interpreted by the web browserand ultimately presented on a user's display. By way of example, HTMLelements may represent headings, paragraphs, hypertext links, embeddedmedia, and a variety of other structures. HTML can include or can loadscripts in languages such as JavaScript, which affect the behavior ofHTML processors such as conventional web browsers, and Cascading StyleSheets (CSS), which define the appearance and layout of text and othercontent. HTML elements are the basic components for HTML and have twobasis properties: attributes and content. Each element's attribute andcontent have certain restrictions that must be followed for an HTMLelement to be considered valid. An HTML element usually has a start tag(e.g., <element-name>) and an end tag (e.g., </element-name>). Theelement's attributes are contained in the start tag and content islocated between the tags (e.g., <element-nameattribute=“value”>Content</element-name>).

By way of example, HTML elements include structural elements (e.g.,describing the purpose of text or other content), presentationalelements (e.g., describing the appearance of text or other contentregardless of its function), and Hypertext elements (e.g., making partof a document into a link to another document). Most elements can takeany of several common attributes. By way of example, the id attributeprovides a document-wide unique identifier for an element, the classattribute provides a way of classifying similar elements, and the titleattribute is used to attach subtextual explanation to an element. HTMLalso defines several data types for element content, such as script dataand stylesheet data, and numerous types for attribute values, including,by way of example, IDs, names, URIs or URLs, numbers, units of length,languages, media descriptors, colors, character encodings, dates andtimes, etc.

Document structure elements include the root element (defined by thestarting and ending tags <html> and </html>, respectively), headelements (defined by the starting and ending tags <head> and </head>,respectively), and body elements (defined by the starting and endingtags <body> and </body>, respectively). The root element tags <html> and</html> delimit the beginning and end of an HTML document, respectively.All other HTML elements of a given HTML document are included within theroot element. The head element tags <head> and </head> generally definea container for processing information and metadata for an HTMLdocument. Example document head elements found within the head elementcontainer include, by way of example and not by way of limitation, thebase element (defined by starting and ending tags <base> and </base>,respectively), which specifies a base uniform resource locator (URL) forall relative href and other links in the HTML document, the link element(defined by starting and ending tags <link> and </link>, respectively),which specifies links to other documents (e.g., for external CSS files),the meta element (defined by starting and ending tags <meta> and</meta>, respectively), which can be used to specify additional metadataabout an HTML document, the object element (defined by starting andending tags <object> and </object>, respectively), used for includinggeneric objects within the document header, the script element (definedby starting and ending tags <script> and </script>, respectively), whichcan act as a container for script instructions (e.g., JavaScript) or alink to an external script with the src (source) attribute, the styleelement (defined by starting and ending tags <style> and </style>,respectively), which specifies a style for the document and which canact as a container for style instructions (e.g., for inlined CSS rules),and the title element (defined by starting and ending tags <title> and</title>, respectively), which defines a document title.

The body element <body> represents a container for the displayablecontent of an HTML document. Example body elements include, by way ofexample and not by way of limitation, block elements (e.g., basic textand list elements, among others), inline elements (e.g., anchor andphrase elements), and image and object elements. A script elementpositioned within the body element may be used to place a script in thedocument (e.g., the script element may contain instructions todynamically generate block or inline content). The image element(defined by starting and ending tags <img> and </img>, respectively) maybe used to insert an image into the document. By way of example, theimage element may include an src attribute that specifies a URL wherethe image is located. The object element (defined by starting and endingtags <object> and </object>, respectively) may be used to insert anobject into the document of the type specified in an included typeattribute. Another frequently used HTML element is the frameset element,which may be used as an alternative to the body element.

Generally, a web application is an application that may be accessed viaa web browser or other client application over a network, or a computersoftware application that is coded in a web browser-supported languageand reliant on a web browser to render the application executable. Webapplications have gained popularity largely as a result of the ubiquityof web browsers, the convenience of using a web browser launched at aremote computing device as a client (sometimes referred to as a thinclient), and the corresponding ability to update and maintain webapplications without distributing and installing software on remoteclients. Often, to implement a web application, the web applicationrequires access to one or more resources provided at a backend server ofan associated website. Additionally, web applications often requireaccess to additional resources associated with other applications.

Social networking system 20 may include a multitude of features withwhich users at remote clients 30 may interact during user sessions. Inparticular embodiments, these features may be implemented as webapplications and may utilize JavaScript and CSS resources requested fromservers 22 as well as other external servers or data stores. The webapplications or resources may be embedded in various web pages served toremote clients, such as in frames or iFrames, sections or “divs” and thelike. In particular embodiments, the social networking system 20maintains in data store 24 a number of objects for the different kindsof items with which a user may interact while accessing socialnetworking system 20. In one example embodiment, these objects includeuser profiles, application objects, and message objects (such as forwall posts, emails and other messages). In one embodiment, an object isstored by the system 20 for each instance of its associated item. Theseobjects and the actions discussed herein are provided for illustrationpurposes only, and it can be appreciated that an unlimited number ofvariations and features can be provided on a social networking system20.

As described above, a web page or underlying structured document may besegmented or divided into sections logically, visually, or otherwise. Byway of example, the structured document used to encode the web page mayinclude one or more block-level elements denoted by starting and endingHTML <div> tags. By way of background, for common web browsers,displayable elements of a web page can be rendered as either block orinline. While all elements are part of the document sequence, blockelements appear within their parent elements as rectangular objects,which do not break across lines, and with block margins, and width andheight properties, which can be set independently of the surroundingelements. Conversely, inline elements are treated as part of the flow ofdocument text; they cannot have margins, width or height set, and dobreak across lines. Inline elements cannot be placed directly inside thebody element; they must be wholly nested within block-level elements.

As another example, a web page may also be split into one or more framesas structurally specified using HTML Frame elements (e.g., denoted bystarting and ending tags <frame> and </frame>, respectively). Framesallow a web browser display window to be split into segments, each ofwhich can show a different document. Another frame element is the inlineframe element (denoting by starting and ending tags <iframe> and</iframe>, respectively). An inline frame places another HTML structureddocument in a frame. Unlike an object element, an inline frame can bethe “target” frame for links defined by other elements.

Hereinafter, any logical, structural, or visual section or portion of aweb page or the structured document used to encode the web page, such asa block-level element, frame, or inline frame, among others, mayhereinafter each be referred to as a “pagelet.”

When a user at a client device (e.g., client device 30) desires to viewa particular web page (hereinafter also referred to as “targetstructured document”) hosted, at least in part, by social networkingsystem 20, the user's web browser, or other client-sidedocument-rendering engine or suitable client application, formulates andtransmits a request to social networking system 20. The requestgenerally includes a URL or other document identifier as well asmetadata or other information. By way of example, the request mayinclude information identifying the user, such as a user ID, as well asinformation identifying or characterizing the web browser or operatingsystem running on the user's client computing device 30. The request mayalso include location information identifying a geographic location ofthe user's client device or a logical network location of the user'sclient device. The request may also include a timestamp identifying whenthe request was transmitted.

A method for serving a request for a web page will now be described withreference to the block diagram of FIG. 2 and the flowchart of FIG. 3. Inan example embodiment, the method begins at 302 with receiving, by aserver 22 or other computing system in social networking system 20, arequest from a client application at a client device 30 for a web pagehosted, at least in part, by social networking system 20. As describedabove, the request generally includes a URL or other document identifiercorresponding to the web page location, as well as metadata or otherinformation. By way of example, the request may include informationidentifying the user of the client application making the request, suchas a user ID, as well as information identifying or characterizing theclient-side document-rendering application (e.g., web browser) 202 oroperating system running on the user's client computing device 30. Therequest may also include location information identifying a geographiclocation of the user's client device or a logical network location ofthe user's client device. The request may also include a timestampidentifying when the request was transmitted. An authentication process204 may first determine, at 304, whether the user making the request isauthorized to receive the requested web page (e.g., has the usersuccessfully logged in and is the user requesting a page for which theuser has access or administrative rights).

In particular embodiments, web page-serving process 206 then analyzesthe request and generates, at 306, a base (skeletal) structured documentusing markup language code (e.g., HTML, XML, or other suitable markuplanguage code). In particular embodiments, the base structured documentincludes a head element (e.g., an HTML head element) and a body element(e.g., an HTML body element). In particular embodiments, the headelement includes an executable code segment for implementing apage-assembling process 208 at the requesting client 30. In particularembodiments, the executable code segment for implementing thepage-assembling process 208 is a JavaScript code segment and includes aJavaScript function library. The head element may also include one ormore initial resources (e.g., JavaScript or CSS) or references to suchresources (e.g., in the form of script, image, or object elements havingcorresponding source (src) identifiers for locating the selectedresources) to be downloaded from external locations (e.g., third partysites). In particular embodiments, it is desirable to minimize thenumber of initial resources included in the base structured document(e.g., to expedite the transmitting of the base structured document tothe requesting client 30). In particular embodiments, the body elementincludes markup language code for rendering one or more place-holdersonce received by the requesting client 30. In particular embodiments,page-serving process 206 adds a place-holder into the base structureddocument for each of one or more (there are generally a plurality)pagelets to be transmitted to the client 30 in corresponding secondresponses, as will be described in more detail below. The body elementmay also include resources, references to resources, or even content tobe rendered once received by the requesting client 30 (although, again,in particular embodiments the resources, reference to resources, orcontent are minimized in the base structured document). In particularembodiments, web page-serving process 206 then formulates and transmitsan initial response or initial response portion (hereinafter alsoreferred to as a “first response” or “first response portion”) at 308 tothe requesting client 30 that includes the base structured document (Itshould be noted that in some embodiments, some data such as, forexample, pre-fetching instructions may be transmitted to the clientprior to transmitting the initial/first response/response portion). Theinitial response may be transmitted to the requesting client 30 over anHTTP or any other suitable connection. In particular embodiments, theconnection over which the initial response is transmitted to the client30 is a persistent Transmission Control Protocol (TCP) connection. Aswill be described below, this enables the client 30 to receive, and tobegin processing of, the base structured document and to initialize ordownload the resources in the initial response while the remainder ofthe requested web page is generated.

In particular embodiments, after, or even at least partially inparallel, with generating the base structured document at 306 ortransmitting the initial response at 308, web page-serving process 206launches, at 310, page-generating process 210 and instructs it togenerate the remainder of the requested web page. In one particularembodiment, page-generating process 210 comprises a master process thatadministers a plurality of subpage-generating processes that are eachconfigured to generate an assigned subportion of the webpage. That is,in particular embodiments, each of one or more subpage-generatingprocesses begins generating an assigned pagelet in parallel with theother subpage-generating processes. In one particular embodiment, aseach subpage-generating process completes the generation of its assignedpagelet, page-generating process 210 passes the pagelet to page-servingprocess 206, which then formulates and transmits the pagelet as asecondary response or secondary response portion (hereinafter alsoreferred to as a “second response” or “second response portion”) at 312to the requesting client 30. In an alternate embodiment, page-servingprocess 206 may comprise page-generating process 210 and may generateeach secondary portion sequentially in-process, which may generally notinvolve launching one or more other page-generating processes. It shouldbe noted that, while described as a single step 312, step 312 maygenerally include the formulating and transmitting of a plurality ofpagelets in a plurality of corresponding secondary responses sent inseries or parallel to client 30, and in some embodiments, as eachpagelet is generated. As described above, each secondary response may betransmitted to the client 30 over the same persistent TCP or othersuitable connection over which the initial response was transmitted. Inone embodiment, the body element of the base structured document may notbe closed with an ending tag, and as such, each secondary response maybe transmitted as a later-generated and later-transmitted part of thebody element of the base structured document. In another embodiment, oneor more of the secondary responses may be transmitted as one or moreindependent HTML responses.

In one embodiment, as described above, each of the secondary responsesor secondary response portions (of which there may generally be aplurality) is formulated and transmitted when the corresponding pageletis completed by page-generating process 210 (or subpage-generatingprocess thereof). In one alternate embodiment, page-generating process210 or page-serving process 206 may transmit the secondary responses inany suitable or preferred order. By way of example, page-serving process206 may order the transmitting of the secondary responses based on theircorresponding importance or relevance in the rendering of the webpage.However, it particular embodiments, as described below, the client-sidepage assembling process 208 may enforce a preferred order of thereceived pagelets and process each pagelet according to a number offactors or preferences.

In particular embodiments, when the requesting client 30, andparticularly document-rendering application 202 (e.g., a web browser)receives the initial response, document-rendering application 202processes the initial response and the base structured document andgenerates a model representation of the base structured document inmemory at the client 30. By way of example, document-renderingapplication 202 may generate a Document Object Model (DOM)representation 212 of the base structured document. As will beappreciated by those of skill in the art, when document-renderingapplication 202 generates the DOM representation 212, it essentiallytranslates the markup language code into a DOM tree or DOM hierarchy ofDOM elements or nodes, each of which may include or contain resources,references for resources, content, among other possibilities. Inparticular embodiments, the base structured document is configured suchthat document-rendering application 202 generates one or more DOM nodesfor each of the place-holders specified in the base structured document.Hereinafter, these DOM nodes may be referred to as “place-holder DOMnodes.” Generally, each place-holder DOM node doesn't include anyresources, references for resources, or content to be displayed,however, these place-holder DOM nodes, when rendered bydocument-rendering application 202 and generally displayed essentiallyreserve places in the rendered base structured document in whichsubsequently received resources, references for resources, or content inassociated pagelets in subsequently received secondary responses will bedisplayed, initialized, or executed, as will be described in more detailbelow.

In particular embodiments, the code segment (e.g., JavaScript) forimplementing page-assembling process 208 is initialized upon beingprocessed by document-rendering application 202. Upon being initialized,page assembling process 208 may then wait for subsequently receivedsecondary responses described above. Any other resources, or referencesto resources, included in the initial response may also be processed,initialized, executed, or downloaded upon being received bydocument-rendering application 202.

In particular embodiments, as each of the secondary response arereceived by document-rendering application 202, page-assembling process208 may place the contents of each corresponding pagelet in queue 214(which may be implemented in a temporary or other suitable memorylocation accessible by page-assembling process 208 or document-renderingapplication 202). Subsequently, page-assembling process 208 may, foreach received secondary response, identify a corresponding place-holderDOM node (or nodes) in the DOM representation 212 and dynamically insertor swap the contents of the pagelet into the DOM representation 212 ator in place of the corresponding place place-holder DOM node. Inparticular embodiments, the page-assembling process 208 may dynamicallyinsert or swap the contents of the pagelet into the DOM representation212 in conjunction with the document-rendering application 202; that is,the document-rendering application 202 may actually insert or swap thecontents in response to a call from page-assembling process 208. Itshould be noted that this insertion or swapping may involve thegeneration of additional DOM nodes in the DOM representation 212 (e.g.,the generation of lower order DOM nodes in the DOM representation 212 ator below the level of the place-holder DOM node corresponding to thepagelet). As the contents of each secondary response is inserted intothe DOM representation 212, the content or resources inserted may thenbe rendered, executed, initialized, or downloaded for rendering bydocument-rendering application 202 and displayed to the user.

In particular embodiments, each pagelet includes, or is in the formatof, a function call that is configured to call page-assembling process208 once received by the client 30. In particular embodiments,page-assembling process 208 includes a function library (e.g., aJavaScript function library) that includes (e.g., JavaScript) functionsthat are to be, or may be, called by function calls in the subsequentlyreceived secondary responses. In particular embodiments, each pageletincludes some markup language code (e.g., HTML) including a script forimplementing the corresponding function call and that identifies thefunctions required by the function library of page-assembling process208. In particular embodiments, each function call includes one or morearguments wrapped in one or more callback functions including, by way ofexample, HTML or other markup language code, an array of JavaScriptresources, an array of CSS resources, and a register that includes alist of (e.g., JavaScript) scripts or code segments to be executed afterthe pagelet is displayed and the resources identified in the pagelet aredownloaded.

In particular embodiments, each function call further includes somemetadata describing some properties of the pagelet and that may be usedby page-assembling process 208 to determine a relative priority of thepagelet. This enables page-assembling process 208 to schedule a relativedisplay order of each of the pagelets received in the secondaryresponses. By way of example, some pagelets may enable features that arepredetermined to not be critical, or not as critical as other featuresor content, and as such, these pagelets may be rendered after other morecritical pagelets. In one simple implementation, each function callfurther includes a “delay flag.” When this delay flag is set to true,this instructs page-assembling process 208 that the pagelet is notrelatively critical and its insertion into the DOM representation 212and subsequent rendering by document-rendering application 202 may bedelayed until other higher priority pagelets are inserted and rendered.More particularly, and as will be described in more detail below, eachpagelet callback function, when received at the client 30, may be heldin queue 214 until other higher priority pagelet callback functions areprocessed or executed. However, in some embodiments, if there are nohigher priority pagelets in queue 212, a lesser priority pageletcallback function may be processed.

In particular embodiments, as described above, to insert the contents ofa particular pagelet received in a secondary response into the DOMrepresentation 212, page-assembling process 208 must identify thecorresponding place-holder DOM node in the DOM representation 212. Inparticular embodiments, this is achieved by including, by page-servingprocess 206, an identifier (ID) parameter with each place-holder in thebase structured document. Similarly, each pagelet generated bypage-generating process 210 includes an ID parameter usable bypage-assembling process 208 to identify the matching or correspondingplace-holder DOM node in the DOM representation 212 into which, or atwhich, the contents of the pagelet are to be inserted or swapped.

A method for executing a pagelet callback function will now be describedwith reference to the flowchart of FIG. 4. In particular embodiments,when a pagelet is received in a secondary response, the correspondingfunction call calls page-assembling process 208 at 402. Page-assemblingprocess 208 then puts the corresponding pagelet callback function inqueue 214, which may already contain pagelet callback functionscorresponding to previously received pagelets received in previoussecondary responses. Here it should be noted that, in particularembodiments, each pagelet callback function may generally include aplurality of callback functions, each configured to or responsible forcompleting a particular task (e.g., downloading CSS resources, renderingHTML, or downloading and executing JavaScript resources). However, inone particular embodiment, the plurality of callback functions receivedin a given secondary response are wrapped in an overlying callbackfunction hereinafter referred to as the pagelet callback function thatmust be called before each callback function wrapped within the pageletcallback function is called. Additionally or alternately,page-assembling process 208 itself may generate, when the pagelet isreceived at the client or when the pagelet's pagelet callback functionis called (or other suitable time), one or more callback functions foreach pagelet that are configured to complete a respective task.Generally, sometime later when the pagelet callback function is up inqueue 214, page-assembling process 208 processes or executes the pageletcallback function (which, as just described, may include processing orexecuting other callback functions within the pagelet callback functionthat are each responsible for one or more of the following steps)including, for example, dynamically loading, at 402, the CSS resources(e.g., setting the string of CSS parameters) included in the pagelet,identifying the corresponding place-holder DOM node in the DOMrepresentation 212 and inserting (or causing document-renderingapplication 202 to insert) the pagelet content into the correspondingplace-holder DOM node at 404 (e.g., translating, or causing thedocument-rendering application 202 to translate, the HTML or othermarkup language code into the DOM representation 212 at or in place ofthe corresponding place-holder DOM node), dynamically loading, at 406,the JavaScript or other resources included in the pagelet that callparticular functions in the function library of page-assembling process208, and executing, at 408, the scripts or other code segmentsidentified in the register. Additionally, any resources that arerequired to be downloaded for a pagelet may be downloaded and theninitialized by, for example, page-assembling process 208. Various eventhandling and event messaging systems or mechanisms may be used totrigger such inter- and intra-callback function operations, particularexamples of which will be described in more detail below with referenceto FIG. 5.

In one particular embodiment, page-serving process 206 orpage-generating process 210 assigns a priority to each pagelet andincludes this priority information as, for example, a “phase” parameteror property in the pagelet's callback function. By way of example, inone implementation, pagelets may be assigned one of three possible phase(priority) parameter values: phase 1 (high priority), phase 2 (mediumpriority), or phase 3 (low priority). This phase information may then beused by page-assembling process 208 to enforce a preferred order ofprocessing the pagelet callback functions corresponding to the pageletsin queue 214. As described above, when each secondary response isreceived at the client 30, the pagelet's function call callspage-assembling process 208, which then puts the pagelet, andparticularly the corresponding pagelet callback function, in queue 214.However, in particular embodiments, page-assembling process 208 onlyprocesses or executes (e.g., loading CSS resources, translating HTML,and loading, initializing, or executing JavaScript or other resources orcode segments) callback functions corresponding to pagelets of a givenphase parameter value at a time; that is, in the above example,page-assembling process 208 doesn't execute the callback functions ofpagelets of phase 3 until the callback functions of pagelets of phase 2are executed and, similarly, the callback functions of pagelets of phase2 aren't executed until the pagelets of phase 1 are executed. In oneexample, page-serving process 206 transmits all the secondary responsesthat include pagelets of phase 1 before transmitting any secondaryresponses that include pagelets of phase 2, and similarly, transmits allthe secondary responses that include pagelets of phase 2 beforetransmitting any secondary responses that include pagelets of phase 3.However, to minimize the time required to render the requested web pageat the client 30, in particular embodiments, the secondary responses areformulated and transmitted as soon as their respective pagelets aregenerated by page-generating process 210 as described with reference toparticular embodiments above. To facilitate the proper or preferredordering of execution in such embodiments, page-serving process 206 maytransmit with the initial response (or subsequently), information thatinforms page-assembling process 208 of the number of pagelets of eachphase. By way of example, in one particular implementation, the totalnumber of phases is transmitted with the initial response and eachpagelet transmitted in a respective secondary response includes a“is_last” flag that, when set to true, informs page-assembling process208 that the respective pagelet is the last pagelet of that particularphase. In yet another alternate embodiment, all the pagelets may betransmitted to the client 30 in a single secondary response.

Thus, generally, and conceptually, to enforce a preferred order ofrendering/displaying by document-rendering application 202, when apagelet callback function is up in the queue 214 for execution,page-assembling process 208 may first check the pagelet's priority; thatis, inspects the pagelet's associated phase value, and then determinewhether there are any other pagelets of higher phase value. If thereare, page-assembling process 208 executes the callback functions of thehigher phase pagelets first. If there are no other pagelets having ahigher phase value, the pagelet at the top of the queue 214 isprocessed. However, in order to not unnecessarily prolong thepage-assembling process, even if all of the callback functions of higherphase pagelets are not executed because they have not yet been receivedby the client 30, callback functions in queue 214 associated with lowerphase pagelets may be executed.

A more detailed description of an example implementation of thepage-assembling method executed by page-assembling process 208 will nowbe described with reference to the flowchart illustrated in FIG. 5. Inone particular embodiment, page-assembling process 208 includes a subarbiter process 216. Arbiter process 216 effectively implements apublish/subscribe system for ordering the processing of pagelet callbackfunctions (inter-callback) as well as the ordering of the processingwithin each callback function (intra-callback). In particularembodiments, when page-assembling process 208 receives, at 502, a callfrom a function call associated with a pagelet received in a secondaryresponse, it registers, at 504, the pagelet's callback function witharbiter process 216 effectively registering the callback function as asubscriber for a set of conditions (e.g., completion of particularevents) that must be satisfied before executing the callback function.In registering a pagelet callback function with arbiter process 216,arbiter process 216 is informed of the associated phase parameter valueassigned to the pagelet, which arbiter process 216 then uses todetermine what conditions need to be satisfied before processing(executing) the callback function. Additionally, in particularembodiments, each process or corresponding function (or callbackfunction) involved with executing the pagelet callback function (e.g.,loading CSS resources, inserting HTML markup language code into DOMrepresentation 212, loading, initializing, downloading, or executingJavaScript resources, code segments or scripts) is also registered witharbiter process 216 at 504. That is, each pagelet callback function mayinclude callback functions for executing the individual processesrequired to execute the overlying pagelet callback function (e.g., acallback function for loading CSS resources, a callback function forinserting HTML markup language code into the DOM representation 212,callback functions for loading, initializing, downloading, or executingthe JavaScript resources, code segments, or scripts, etc.). As describedabove, these individual or sub-pagelet callback functions may be wrappedwithin a pagelet callback function by page-serving process 206 orpage-generating process 210 or, additionally or alternately, may begenerated by page-assembling process 208 itself after receiving therespective pagelet callback function.

In particular embodiments, at some point after receiving a first callfrom a first received function call corresponding to a first receivedpagelet received in a first secondary response, page-assembling process208 then executes, at 506, the callback function corresponding to thefirst received pagelet having a phase parameter value of 1. As describedabove with reference to FIG. 4, executing the callback function at 506may first involve calling a function that dynamically loads the CSSresources included in the pagelet callback function arguments (step 402in FIG. 4). When the CSS resources are loaded, a “CSS resource loadingdone” signal may then be sent to arbiter 216. Upon receipt of the CSSresource loading done signal, a function for inserting (or causingdocument-rendering application 202 to insert) the pagelet content intothe corresponding place-holder DOM node (step 404 in FIG. 4) is calledby arbiter process 216. Upon completion of the insertion of the content,a “content insertion done” signal may then be sent to arbiter process216. Upon receipt of the content insertion done signal, a function fordynamically loading the JavaScript or other resources included in thepagelet that call particular functions in the function library ofpage-assembling process 208 (step 406 in FIG. 4) may then be called byarbiter process 216. Upon completion of the loading of the JavaScriptresources that call particular functions in the function library ofpage-assembling process 208, a “JavaScript loading done” signal may thenbe sent to arbiter process 216. Upon receipt of the JavaScript loadingdone signal, a function for executing the scripts or other code segmentsidentified in the register of the pagelet callback function (step 408 ofFIG. 4) may then be called by arbiter process 216. Upon completion ofthe execution of the scripts or other code segments in the register, a“register execution done” signal may then be sent to arbiter process216. Upon receipt of the register execution done signal, arbiter process216 then determines, at 508, whether or not all the callback functionsassociated with pagelets of phase 1 have been executed. If not, themethod proceeds back to 506 with executing the next callback functioncorresponding to a pagelet of phase 1. If all of the callback functionsassociated with pagelets of phase 1 have been executed, a “phase 1 done”signal is sent to arbiter process 216.

In an example implementation, in response to the “phase 1 done” signal,arbiter process 216 then calls the callback function associated with thenext pagelet of phase 2, which then gets executed at 510 as describedabove. Arbiter process 216 then determines, at 512, whether or not allthe callback functions associated with pagelets of phase 2 have beenexecuted. If not, the method proceeds back to 510 with executing thenext callback function corresponding to a pagelet of phase 2. If all ofthe callback functions associated with pagelets of phase 2 have beenexecuted, a “phase 2 done” signal is sent to arbiter process 216.Similarly, in an example, implementation, arbiter process 216 then callsthe callback function associated with the next pagelet of phase 3, whichthen gets executed at 514 as described above. Arbiter process 216 thendetermines, at 516, whether or not all the callback functions associatedwith pagelets of phase 3 have been executed. If not, the method proceedsback to 514 with executing the next callback function corresponding to apagelet of phase 3. If all of the callback functions associated withpagelets of phase 3 have been executed, a “phase 3 done” signal is sentto arbiter process 216.

It should be noted that, in particular alternate embodiments, callbackfunctions associated with pagelets of the same phase may be executed inparallel. More particularly, to exploit parallelism among pagelets, theexecution of pagelets with the same phase/priority may be highlyparallelized. For example, if pagelet A and pagelet B have the samepriority, the CSS resources for each of pagelet A and pagelet B may bothbe downloaded at least partially simultaneously (e.g., the CSS resourcesfor pagelet A may be begin loading simultaneously or concurrently withthe loading of the CSS resources for pagelet B) and thereafter havetheir respective content displayed without waiting for the otherpagelet's (pagelet A or pagelet B) operations. However, continuing thisexample, if a pagelet C has lower priority than pagelets A and B, theexecution of pagelet C (or particularly the callback function of pageletC) may not be executed until both pagelet A and pagelet B have beenexecuted (e.g., rendered and displayed).

Additionally, in particular embodiments, the downloading or execution ofJavaScript resources or code segments is not done in phases; that is, inparticular embodiments, the JavaScript resources of all the pagelets arenot downloaded or executed until the rest of the functions or callbackfunctions within the pagelet callback functions have executed. In otherwords, the display of the pagelets may be phased, but the downloading orexecution of JavaScript may be done in one batch. By way of example, inone implementation, the flow may be as follows: download CSS resourcesfor pagelets of phase 1, display pagelets of phase 1, download CSSresources for pagelets of phase 2, display pagelets of phase 2, downloadCSS resources for pagelets of phase 3, display pagelets of phase 3,download JavaScripts resources for all pagelets, and execute JavaScriptresources for all pagelets (in such an implementation, in each phase, apagelet's display may only wait for its own CSS resources to bedownloaded, but not for other pagelets' CSS resources to be downloaded).That is, in particular embodiments, it is only the individualsub-pagelet callback functions responsible for downloading CSS resourcesand rendering HTML that govern (or wait for) the phase 1, 2, or 3 donesignals. In contrast, in particular embodiments, the downloading andexecution of JavaScripts may only be performed after all the pageletsare displayed (e.g., after the CSS resources for all the pagelets aredownloaded and the HTML for all the pagelets is rendered).

As described herein, any of the described processes or methods can beimplemented as a series of computer-readable instructions, embodied orencoded on or within a tangible data storage medium, that when executedare operable to cause one or more processors to implement the operationsdescribed above. For smaller datasets, the operations described abovecan be executed on a single computing platform or node. By way ofexample, in particular embodiments, the phased generation processesdescribed above with reference to FIGS. 2 and 3 may be implemented by asingle server process executing in server 22. That is, the web pagegeneration and serving processes described above may be implemented onserver 22. For larger systems and resulting data sets, parallelcomputing platforms can be used.

FIG. 1 illustrates an example distributed computing system, consistingof one master server 22 a and two slave servers 22 b. In someembodiments, the distributed computing system comprises ahigh-availability cluster of commodity servers in which the slaveservers are typically called nodes. Though only two nodes are shown inFIG. 1, the number of nodes might well exceed a hundred, or even athousand or more, in some embodiments. Ordinarily, nodes in ahigh-availability cluster are redundant, so that if one node crasheswhile performing a particular application, the cluster software canrestart the application on one or more other nodes.

Multiple nodes also facilitate the parallel processing of largedatabases. In some embodiments, a master server, such as 22 a, receivesa job from a client and then assigns tasks resulting from that job toslave servers or nodes, such as servers 22 b, which do the actual workof executing the assigned tasks upon instruction from the master andwhich move data between tasks. In some embodiments, the client jobs willinvoke Hadoop's MapReduce functionality, as discussed above.

Likewise, in some embodiments, a master server, such as server 22 a,governs a distributed file system that supports parallel processing oflarge databases. In particular, the master server 22 a manages the filesystem's namespace and block mapping to nodes, as well as client accessto files, which are actually stored on slave servers or nodes, such asservers 22 b. In turn, in some embodiments, the slave servers do theactual work of executing read and write requests from clients andperform block creation, deletion, and replication upon instruction fromthe master server.

While the foregoing processes and mechanisms can be implemented by awide variety of physical systems and in a wide variety of network andcomputing environments, the server or computing systems described belowprovide example computing system architectures for didactic, rather thanlimiting, purposes.

FIG. 6 illustrates an example computing system architecture, which maybe used to implement a server 22 a, 22 b, or a client device 30. In oneembodiment, hardware system 600 comprises a processor 602, a cachememory 604, and one or more executable modules and drivers, stored on atangible computer readable medium, directed to the functions describedherein. Additionally, hardware system 600 includes a high performanceinput/output (I/O) bus 606 and a standard I/O bus 608. A host bridge 610couples processor 602 to high performance I/O bus 606, whereas I/O busbridge 612 couples the two buses 606 and 608 to each other. A systemmemory 614 and one or more network/communication interfaces 616 coupleto bus 606. Hardware system 600 may further include video memory (notshown) and a display device coupled to the video memory. Mass storage618, and I/O ports 620 couple to bus 608. Hardware system 600 mayoptionally include a keyboard and pointing device, and a display device(not shown) coupled to bus 608. Collectively, these elements areintended to represent a broad category of computer hardware systems,including but not limited to general purpose computer systems based onthe x86-compatible processors manufactured by Intel Corporation of SantaClara, Calif., and the x86-compatible processors manufactured byAdvanced Micro Devices (AMD), Inc., of Sunnyvale, Calif., as well as anyother suitable processor.

The elements of hardware system 600 are described in greater detailbelow. In particular, network interface 616 provides communicationbetween hardware system 600 and any of a wide range of networks, such asan Ethernet (e.g., IEEE 802.3) network, a backplane, etc. Mass storage618 provides permanent storage for the data and programming instructionsto perform the above-described functions implemented in the servers 22a, 22 b, whereas system memory 614 (e.g., DRAM) provides temporarystorage for the data and programming instructions when executed byprocessor 602. I/O ports 620 are one or more serial and/or parallelcommunication ports that provide communication between additionalperipheral devices, which may be coupled to hardware system 600.

Hardware system 600 may include a variety of system architectures; andvarious components of hardware system 600 may be rearranged. Forexample, cache 604 may be on-chip with processor 602. Alternatively,cache 604 and processor 602 may be packed together as a “processormodule,” with processor 602 being referred to as the “processor core.”Furthermore, certain embodiments of the present invention may notrequire nor include all of the above components. For example, theperipheral devices shown coupled to standard I/O bus 508 may couple tohigh performance I/O bus 606. In addition, in some embodiments, only asingle bus may exist, with the components of hardware system 600 beingcoupled to the single bus. Furthermore, hardware system 600 may includeadditional components, such as additional processors, storage devices,or memories.

In one implementation, the operations of the embodiments describedherein are implemented as a series of executable modules run by hardwaresystem 600, individually or collectively in a distributed computingenvironment. In a particular embodiment, a set of software modulesand/or drivers implements a network communications protocol stack,parallel computing functions, browsing and other computing functions,optimization processes, and the like. The foregoing functional modulesmay be realized by hardware, executable modules stored on a computerreadable medium, or a combination of both. For example, the functionalmodules may comprise a plurality or series of instructions to beexecuted by a processor in a hardware system, such as processor 602.Initially, the series of instructions may be stored on a storage device,such as mass storage 618. However, the series of instructions can betangibly stored on any suitable storage medium, such as a diskette,CD-ROM, ROM, EEPROM, etc. Furthermore, the series of instructions neednot be stored locally, and could be received from a remote storagedevice, such as a server on a network, via network/communicationsinterface 616. The instructions are copied from the storage device, suchas mass storage 618, into memory 614 and then accessed and executed byprocessor 602.

An operating system manages and controls the operation of hardwaresystem 600, including the input and output of data to and from softwareapplications (not shown). The operating system provides an interfacebetween the software applications being executed on the system and thehardware components of the system. Any suitable operating system may beused, such as the LINUX Operating System, the Apple Macintosh OperatingSystem, available from Apple Computer Inc. of Cupertino, Calif., UNIXoperating systems, Microsoft® Windows® operating systems, BSD operatingsystems, and the like. Of course, other implementations are possible.For example, the functions described herein may be implemented infirmware or on an application specific integrated circuit.

Furthermore, the above-described elements and operations can becomprised of instructions that are stored on storage media. Theinstructions can be retrieved and executed by a processing system. Someexamples of instructions are software, program code, and firmware. Someexamples of storage media are memory devices, tape, disks, integratedcircuits, and servers. The instructions are operational when executed bythe processing system to direct the processing system to operate inaccord with the invention. The term “processing system” refers to asingle processing device or a group of inter-operational processingdevices. Some examples of processing devices are integrated circuits andlogic circuitry. Those skilled in the art are familiar withinstructions, computers, and storage media.

The present disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsherein that a person having ordinary skill in the art would comprehend.Similarly, where appropriate, the appended claims encompass all changes,substitutions, variations, alterations, and modifications to the exampleembodiments herein that a person having ordinary skill in the art wouldcomprehend. By way of example, while embodiments of the presentdisclosure have been described as operating in connection with a socialnetworking website, various embodiments of the present invention can beused in connection with any communications facility that supports webapplications. Furthermore, in some embodiments the term “web service”and “web site” may be used interchangeably and additionally may refer toa custom or generalized API on a device, such as a mobile device (e.g.,cellular phone, smart phone, personal GPS, personal digital assistance,personal gaming device, etc.), that makes API calls directly to aserver.

What is claimed is:
 1. A method comprising: receiving, by a computingserver machine, a request for a web page; sending, by the computingserver machine, a first response portion for generating the requestedweb page to a client computing device in response to the request, thefirst response portion comprising a structured document for use by theclient computing device to render the requested web page, the structureddocument comprising: markup-language code that comprises one or moreplace-holder code segments; and an executable code segment forimplementing a page-assembling process; generating, by the computingserver machine, one or more second response portions each for generatinga corresponding portion of the requested web page, each second responseportion comprising markup-language code comprising a call to a functionof the page-assembling process; determining, for each second generatedsecond response portion, a relative priority; sending, by the computingserver machine, each of the second response portions to the clientcomputing device in an order based on the determined relative prioritiesof the respective second response portions, wherein each second responseportion is configured to be inserted at a location determined by acorresponding one of the place-holder code segments of the structureddocument; and wherein the page-assembling process is configured to, foreach second response portion: identify a place-holder identification(ID) parameter in the respective call to the function; access a modelrepresentation of the structured document, wherein the modelrepresentation comprises one or more place-holder code segments, eachplace-holder code segment having a corresponding place-holder IDparameter; identify a particular place-holder segment in the modelrepresentation by matching the place-holder ID parameter in therespective call to the function to a place-holder segment having amatching place-holder ID parameter; and insert, or cause to be inserted,at the respective location determined by the particular place-holdercode segment, the second response portion into the model representationof the structured document generated by a client rendering application.2. The method of claim 1, wherein the structured document furthercomprises one or more first resources or one or more first references tofirst resources.
 3. The method of claim 1, wherein the one or moresecond response portions further comprise one or more of: one or moresecond portions of content to be rendered by the client computingdevice, one or more second resources, or one or more second referencesto second resources to be downloaded.
 4. The method of claim 1, whereinthe page-assembling process is implemented at the client computingdevice.
 5. The method of claim 1, wherein generating each of the one ormore second response portions comprises causing each of a plurality ofpage-generating processes to generate the markup-language code, one ormore second portions of content, one or more second resources, or one ormore second references to second resources, and the call to the functionin a corresponding second response portion at least partially inparallel.
 6. The method of claim 5, wherein each of the one or moresecond response portions are sent to the client computing device uponcompletion of the generating of the markup language code, one or moresecond portions of content, one or more second resources, or one or moresecond references to second resources, and the call to the function inthe respective second response portion.
 7. The method of claim 1,wherein the page-assembling process is further configured to: determinewhether one or more conditions that must be satisfied before executingthe call to the function have been met.
 8. The method of claim 1,wherein after each of the one or more second response portions arereceived by the client computing device, the call to the function ofeach second response portion is configured to call the page-assemblingprocess.
 9. The method of claim 1, wherein each second response portioncomprises an identifier parameter that is usable by the page-assemblingprocess to identify the corresponding place-holder code segment in thestructured document.
 10. The method of claim 1, wherein when the firstresponse portion is received by the client computing device, the firstresponse portion is configured to cause the client rendering applicationexecuting in the client computing device to generate the modelrepresentation of the structured document for rendering the structureddocument, and to begin downloading or executing one or more firstresources or one or more first references to first resources.
 11. Themethod of claim 1, wherein each place-holder code segment is representedas a place-holder node in the model representation.
 12. The method ofclaim 1, wherein each second response portion comprises a callbackfunction that comprises the markup language code, one or more secondportions of content, one or more second resources, or one or more secondreferences to second resources.
 13. The method of claim 12, wherein thepage-assembling process executes the callback functions of the secondresponse portions each having a highest priority parameter value beforeexecuting callback functions of the second response portions not havingthe highest priority parameter value.
 14. A computing server machinecomprising: one or more processors; and a memory coupled to theprocessors comprising instructions executable by the processors, theprocessors being operable when executing the instructions to: receive arequest for a web page; send a first response portion for generating therequested web page to a client computing device in response to therequest, the first response portion comprising a structured document foruse by the client computing device to render the requested web page, thestructured document comprising: markup-language code that comprises oneor more place-holder code segments; and an executable code segment forimplementing a page-assembling process; generate one or more secondresponse portions each for generating a corresponding portion of therequested web page, each second response portion comprisingmarkup-language code comprising a call to a function of thepage-assembling process; determine, for each second generated secondresponse portion, a relative priority; send each of the second responseportions to the client computing device in an order based on thedetermined relative priorities of the respective second responseportions, wherein each second response portion is configured to beinserted at a location determined by a corresponding one of theplace-holder code segments of the structured document; and wherein thepage-assembling process is configured to, for each second responseportion: identify a place-holder identification (ID) parameter in therespective call to the function; access a model representation of thestructured document, wherein the model representation comprises one ormore place-holder code segments, each place-holder code segment having acorresponding place-holder ID parameter; identify a particularplace-holder segment in the model representation by matching theplace-holder ID parameter in the respective call to the function to aplace-holder segment having a matching place-holder ID parameter; andinsert, or cause to be inserted, at the respective location determinedby the particular place-holder code segment, the second response portioninto the model representation of the structured document generated by aclient rendering application.
 15. The computing server machine of claim14, wherein the structured document further comprises one or more firstresources or one or more first references to first resources.
 16. Thecomputing server machine of claim 14, wherein the one or more secondresponse portions further comprise one or more of: one or more secondportions of content to be rendered by the client computing device, oneor more second resources, or one or more second references to secondresources to be downloaded.
 17. The computing server machine of claim14, wherein the processors being operable when executing theinstructions to generate each of the one or more second responseportions comprises the processors being operable when executing theinstructions to: cause each of a plurality of page-generating processesto generate the markup language code, one or more second portions ofcontent, one or more second resources, or one or more second referencesto second resources, and the call to the function in a correspondingsecond response portion at least partially in parallel.
 18. Thecomputing server machine of claim 17, wherein each of the one or moresecond response portions are sent to the client computing device uponcompletion of the generating of the markup language code, one or moresecond portions of content, one or more second resources, or one or moresecond references to second resources, and the call to the function inthe respective second response portion.
 19. One or morecomputer-readable non-transitory storage media embodying software thatis operable when executed to: receive, by a computing server machine, arequest for a web page; send, by the computing server machine, a firstresponse portion for generating the requested web page to a clientcomputing device in response to the request, the first response portioncomprising a structured document for use by the client computing deviceto render the requested web page, the structured document comprising:markup-language code that comprises one or more place-holder codesegments; an executable code segment for implementing a page-assemblingprocess; generate, by the computing server machine, one or more secondresponse portions each for generating a corresponding portion of therequested web page, each second response portion comprisingmarkup-language code comprising a call to a function of thepage-assembling process; determine, for each second generated secondresponse portion, a relative priority send, by the computing servermachine, each of the second response portions to the client computingdevice in an order based on the determined relative priorities of therespective second response portions, wherein each second responseportion is configured to be inserted at a location determined by acorresponding one of the place-holder code segments of the structureddocument; and wherein the page-assembling process is configured to, foreach second response portion: identify a place-holder identification(ID) parameter in the respective call to the function; access a modelrepresentation of the structured document, wherein the modelrepresentation comprises one or more place-holder code segments, eachplace-holder code segment having a corresponding place-holder IDparameter; identify a particular place-holder segment in the modelrepresentation by matching the place-holder ID parameter in therespective call to the function to a place-holder segment having amatching place-holder ID parameter; and insert, or cause to be inserted,at the respective location determined by the particular place-holdercode segment, the second response portion into the model representationof the structured document generated by a client rendering application.20. The media of claim 19, wherein the one or more second responseportions further comprise one or more of: one or more second portions ofcontent to be rendered by the client computing device, one or moresecond resources, or one or more second references to second resourcesto be downloaded.